Substantial Calefaction
by Angel Gidget
Summary: It's a struggle won for warmth and a battle lost for propriety when it falls to Tessa to keep Jem from freezing to death on a hunt.


**Disclaimer: **Totally not mine.

**Summary: **It's a struggle won for warmth and a battle lost for propriety when it falls to Tessa to keep Jem from freezing to death on a hunt.

**A/N: **Sexytimes for survival in sub zero is one of the oldest tricks in the book, and I had to use it some time. Written for mrscarstairs to make her week better.

_Body-heat_. A simple phrase, that grows louder in her head with its relevance.

There's a little match boy in Tessa's head, one of the dozens of unfortunates the Dark Sisters used in their training. Young Robbie knows that tucking the little kitten against his bare stomach was the only thing that kept it alive for as long as it did, and Tessa knows that young Robbie died because there was no similar source of heat for him on the night he met his end.

Tessa hopes she is enough for Jem, as she strips them both down, blushing terribly along the way.

They were separated from the others while hunting a demon. Will had protested that she shouldn't come, but Gideon had reminded him that she needed to put her training to use at some point, and better now with a full contingent, than later when their numbers might be divided.

But they couldn't have known there would be more than one. And that the chase would split her and Jem from the rest, and end with Jem wounded, and shoved into the ice-cold Thames.

It was as if her mind had snapped into a terrified sort of purposefulness. She'd taken Camile's form, and using the vampiress's strength and whiles, had pulled her unconscious fiancé from the dark drink, and carried him to a downworlder den, one street away.

The iffrit running the place had given them strange looks, but upon the realization that it was a matter of _saving_ a shadowhunter, and thereby _avoiding_ trouble, she'd given them blankets and left them in what appeared to be a set-off room with cushions and dining tables.

The moment she feels Jem's frozen skin against her own, she flinches, nearly jerking back entirely. She forces Camile's form to slip away, she needs _heat_ now, not strength. She is down to her chemise, and Jem is down to his trousers.

She is torn between the thought that it may be all too much or not nearly enough.

But then he shivers. Finally, finally. Because shivering means he will live, and though the cold leaves her feeling numb herself for a moment, in another instant, she can feel his heart beat, and she rubs his arms and his back frantically, urging him to wake.

"T-Tessa?"

"Oh, thank God. Thank God, Jem..."

She wraps her whole self around him. They are surrounded by the blankets that smell like sweat and pepper and a few spices she can't name. He is shaking like a leaf in a thunderstorm, and looking at her like he can't quite believe she's real.

"Th-the d-demon...?"

"Dead. You killed it. But it tossed you into the water. I- I brought us here. Just... just try to warm up, alright? I-"

He kisses her. It's not his best kiss. His mouth is cold, and a little too hard on hers, like he can't quite feel properly yet. But there's strength behind it, and that fact alone gives her hope.

As she lays her cheek against his, she feels tiny tendrils of ice at her temple, and realizes it's his hair, still damp with river water. She runs her hands through it, and unthinkingly, opens her mouth to release heated breath against his his jaw, his ears, his neck. Not unlike the way she would warm her own hands in a cold room, before the fire would take hold.

His grip on her tightens almost painfully, and she hears his moan, though it's soft as a whisper.

"You have no idea... how very badly I wish I could feel everything right now."

Her only response is to laugh and cling tighter, and they stay like that, the seconds lengthening into minutes, the minutes lengthening into something longer.

The longer they stay, the more he shifts. Splaying his hands, wrapping them into fists, and splaying them again. His legs move the most, yet when he finally has them untangled from hers, it feels unnatural, and she can see his back is too curved, that the position can't be any more pleasant for him than for her.

So she reaches forth, and yanks his hips back towards her own, it's only after she's done so that she realizes what she's done. And as she looks into his flushed face, she feels an equivalent red tinge her own. It slips into her mind like flour through a sieve, that there is a pressure between her thighs, and that it grows in intensity from without and from within.

"Tiān-shǐ. I- I can-" He ducks his head as if to move away, and it is the most imperative instinct to grip his Marked shoulder, to keep him from leaving.

So he stops, and meets her eyes.

Tessa realizes that she is the one shivering. It's only natural, then, to lean in towards his warmth. His eyes are silver as ever, but darkened by the light, and by the war between safe behavior and burning curiosity, a war that Tessa has always understood too well.

He secures the blanket over them both as he turns, and his weight settles on her, warmer than a fire-lit hearth. His palms cup her cheeks as he kisses her, and it is slow, so slow, and so warm that it makes no sense for her to be shaking so, but there is no real surprise in that.

When he pulls back again, Tessa feels heat uncurl throughout her veins as she breathes in and out. Even the small movements of her lungs make her terribly aware of the way her stomach touches his through thin cotton one moment, and falls away the next.

She sees him swallow, and watches his eyes for the moment that curiosity drives propriety into the dust. She feels his spine flex beneath her fingers before she feels his hips pivot, surging forward in a circle. Tessa's head falls back, bursts of light stopping and starting behind her eyes. No sooner has she taken breath than she finds herself pushing back, and the compression is undiluted pleasure.

Chapped lips caress her jaw and the underside of her chin, till she feels heated breath carefully blown over her skin, like a favor returned. Only now, Tessa realizes the affect of it, how it teases and spikes rather than soothes.

Her training in the last several weeks has made her stronger, and as her grip on his back tightens, he gives a tiny flinch and her eyes open wide, wondering if her nails have drawn blood. But he merely kisses her again, lightly, and gives a tiny shake of his head.

"Wǒ méishì. No harm done."

Damp strands hang over his brow, and as they turn again to their sides, she reaches up to brush them away. But her hand does not leave his face, instead her thumb strokes the skin beneath his eyes, watching them close as he sighs.

After everything she's felt to this point, a part of Tessa aches now, and only the tiniest squeeze from her legs provides the invitation Jem needs to thrust forward again.

"Jem." It's more of a sigh than a statement, a breath she releases for the joy of saying his name.

His smile starts small, and grows, shining out of him.

She starts to shake all over again when he lays a hand low upon her calf. She knows how sensitive the backs of her own knees are, and she only knows it because Jem's hands have been there before. It's only befitting then that she lays her own hands at the base of his shoulders, slipping down to stroke the equilibrium rune along his tailbone.

Whatever sound he makes is muffled into her shoulder, but it remains deep and low.

Jem is the slightest bit taller than her, but they are still of a height, so it is easy to mirror his movements, to lay her own hands on his legs, though they are still covered in damp cloth.

But individual movements begin to slip away, as he pulls back to kiss her. Hard provoking kisses on her neck, teasing nips at her chin, soft flutters next to her eyes, an exploratory peck at her nose, one deep breathless union of their mouths.

They are both damp with the Thames, and now also with sweat, and she wonders distantly if that should bother her, but the question alone makes her realize that it does not. Because she plans to get used to this, in all its forms. She feels the warmth of his Marked skin where her own is exposed, and where it isn't, she can feel a cool ring of jade lodged against her breast. Her heart beats against it, as if trying to touch it through her skin. Home ceased to be New York long ago. Home is here in London, and every day, it becomes more so because it is where Jem resides.

Tessa hazily realizes that stuttered movements turned into a rhythm when she wasn't watching, that their bodies are moving in a wave, and even the way their panting mouths nearly brush one another's has formed a pattern all its own. She hears her name through the rush of blood in her ears, a whispered yet ardent litany, intermixed with breathy vowels and mystery consonants.

Every sensation seems to swirl and tighten, condensing into singular lattice inside. There is a cry bubbling up inside her, and she swears that one more move with shatter the walls holding it back.

But no sooner does she think it, than all the movements cease.

"... Carstairs! Miss Gray!"

It's Gideon's voice. Muffled by walls and fog, but still far FAR too close.

Jem pulls back to listen, rising to his knees. A drop of water-from his own sweat or hers or the river, she can't tell-falls from his clavicle to his chest, creating what strikes Tessa as a rather mournful train down his stomach. She hates the whine that slips from her throat. It is childish and pointless and unnecessary, but it escapes from her nonetheless. He looks down to her then, and his smile matches her emotions beyond its ironic sort of ruefulness. Desire for desire and disappointment for disappointment.

His gaze flicks to his arm and he shakes his head.

"Damn."

It takes a moment for Tessa to realize that it is his own parabatai rune which has incurred his half-hearted wrath.

"C'mon, James! I know you're here somewhere you sneaky bastard."

Of course. If Jem can use it to track Will, then the reverse shall also prove true.

Damn indeed.

Jem's clothes aren't as dry as they'd like, but he insists that the cold 'helps calm things down'. Tessa declines to ask for further explanation. Their proprietress glares daggers as them as they leave, asking if there is anything other than water in her blankets.

Tessa's still not quite clear on exactly what other than water there would be, but Jem assures the woman there is not.

They take their leave, allowing the frigid night air to explain the flush of their cheeks as they hold hands.

Before leaving, Charlotte always insists that her charges are equipped with coin as well as blade.

So when Tessa sees a little match boy along the path of their carriage, she asks to stop, and buys a box, slipping the child a little extra before turning back.

She feels nervous and fluttery still, but she whispers it on the London wind, hoping the boy will hear it even as she turns back to the carriage, back to Jem.

"Stay warm."

_-f.i.n.-_


End file.
